Apparatus comprising at least one infra-red sensor for detecting people passing through a doorway are known in the art. Normally the apparatus is connected to an alarm to indicate that a person entered or left through the doorway. It will be appreciated that such an apparatus, if connected to a counter, may be utilized to count people passing through the doorway. However, such an arrangement is not adapted to distinguish between people passing in one direction through the doorway and people passing in an opposite direction through the doorway. Furthermore, the known apparatus can also not sense when more than one person pass through the doorway simultaneously or accurately differentiate between people during high flow volumes, so that accurate counting is difficult if not impossible. Neither can such apparatus discriminate between people moving through the doorway and shopping carts, for example, they may happen to be pushing.